Combination tools don't work as well as a tool that is specifically designed for one task. If the cane is a mobility aid, then adding the weight of a sword blade is going to be irritating over the course of a day. The fit is going to have to be quality, or it will rattle. And the joint with the locking mechanism is a potential failure point that will be under stress with every step. If I needed a cane to make sure I stay upright, I wouldn't choose a sword cane even if there weren't significant legal penalties.
The blades in them are usually more like elongated poignards than an edged weapon, Cold Steel was quite proud of putting an actual rapier style blade in one of theirs. They are quite deadly weapons, but the irony is that a rapier or smallsword blade relies on footwork to keep the point engaged with the target at an effective distance. So you take away your mobility aid to deploy a weapon that is more mobility dependent than just using the cane as an impact tool. If the sword cane is just man jewelry, then that's not an issue. Any sharp steel is going to make an attacker think twice, but the money involved in getting a reliable sword cane could go to a Blackthorne cane on the low end, or a one of those super classy titanium war hammer canes on the high end.